Passive Intermodulation (PIM) occurs when signals are present in a passive device that exhibits some non-linear behavior. In a wireless communication device, such as a base station in a wireless communication network, PIM occurs when a high power transmit signal is passed through a passive device that exhibits some non-linearity. This non-linear passive device is referred to as a PIM source. The PIM source may be a non-linear component in a transmit path of the wireless communication device such as, for example, a cable, a connector, a duplex filter, an antenna of the wireless communication device, or even rusty bolt and the like. The PIM source may alternatively be due to an object that is external to the wireless communication device (e.g., a fence). The wireless communication device may have multiple PIM sources.
The PIM created by a PIM source includes multiple Intermodulation Products (IMPs) (e.g., 2nd order, 3rd order, etc.) of the transmit signal. The PIM degrades the wanted signal, in terms of quality and purity. When any of the IMPs fall within a passband of a receiver of the wireless communication device, a resulting PIM distortion is introduced into the received signal and, as a result, the receiver is desensitized. When the receiver's is desensitized, its performances and data-throughput degrade.
PIM distortion is particularly problematic for multi-carrier or multi-band wireless communication devices, such as the new generation of high-power wideband (WB) multi-RAT and multiband wireless communication base stations. Multi-carrier or multi-band signals are an important characteristic of modern wireless communication standards (e.g., the Long Term Evolution (LTE) cellular communication standard) as well as multi-standard, or multi-band, wireless communication devices.
Furthermore, PIM may result in high level of electromagnetic wave emissions, which may exceed the regulatory limit of emissions for radio systems. As such, the radio systems may fail to meet the regulations regarding the emissions. Also, the emissions could cause interference to other radio systems that are co-located at the same site. They may interfere with other UpLink (UL) links of a same radio system, which has diversity at the receiver (Rx) or with Multi Input Multi Output (MIMO) operation.
As such, PIM distortion and emission are becoming an increasingly important problem that needs to be addressed.